In licensed-assisted access using LTE (Licensed-Assisted Access using LTE, LAA-LTE for short), a licensed spectrum is used as a primary component carrier (Primary Component Carrier, PCC) and an unlicensed spectrum is used as a secondary component carrier (Secondary Component Carrier, SCC) based on a carrier aggregation technology to offload data services on the licensed spectrum, to effectively increase a data transmission rate and implement hotspot coverage. In an LAA-LTE system, a channel resource is used based on a channel access mechanism of listen before talk (Listen Before Talk, LBT for short). To be specific, a sending node first performs clear channel assessment (Clear Channel Assessment, CCA for short) before sending a signal, and can occupy a channel to send the signal only after detecting that the channel is idle.
In a signal sending process, a sounding reference signal (Sounding Reference Signal, SRS for short) in uplink transmission is used to estimate quality of uplink channels with different frequencies. Estimated channel quality may be used for scheduling of uplink transmission, and a resource block with a relatively good channel state is allocated for uplink transmission. In addition, the estimated channel quality is used for selection between different transmission parameters such as an instantaneous data rate.
However, an SRS transmission mechanism in an existing LTE system is not perfect and cannot meet a requirement of signal transmission in the LAA-LTE system.